Title: Rho-pion transition form factors in the $k_T$ factorization formulism revisited Show Chinese title

Title: rho介子过渡形式因子在$k_T$因子化公式中的重新研究

Abstract: We revisit the evaluations for the spacelike and timelike $\rho \pi$ transition form factors $F_{\rho\pi}(Q^2)$ and $G_{\rho\pi}(Q^2)$ with the inclusion of the the next-to-leading order (NLO) QCD contributions in the framework of the $k_T$ factorization theorem. The infrared divergence is regularized by the transversal momentum carried by external valence quarks, and ultimately absorbed into the meson wave functions. In the region of $ Q^2 \leqslant 2 \, \textrm{GeV}^2 $, where PQCD factorization apporach applicable, the NLO contribution can bring no larger than $ 35\%$ enhancement to the spacelike form factor $F_{\rho\pi}(Q^2)$. For the timelike form factor derived under the kinematic exchanging symmetry, this contribution is also under control when the momentum transfer squared is large enough. We also prolong our prediction into the small $Q^2$ region by taking the Lattice QCD results into account, and subsequently obtain the coupling $g_{\rho\pi\gamma} = G_{\rho\pi}(0)=0.596$. Show Chinese abstract

Abstract: 我们重新评估了在包含下一阶QCD贡献的框架下，类空和类时$\rho \pi$转换形式因子$F_{\rho\pi}(Q^2)$和$G_{\rho\pi}(Q^2)$的评价，基于$k_T$因子化定理。 红外发散通过外部价夸克携带的横向动量进行正则化，并最终被吸收进介子波函数中。 在$ Q^2 \leqslant 2 \, \textrm{GeV}^2 $区域内，当PQCD因子化方法适用时，NLO贡献对类空形式因子$F_{\rho\pi}(Q^2)$的增强不超过$ 35\%$。 对于在运动学交换对称性下推导出的类时形式因子，当动量转移平方足够大时，这一贡献也是可控的。 我们还将预测延伸到小 $Q^2$ 区域，同时考虑格点QCD的结果，随后得到耦合 $g_{\rho\pi\gamma} = G_{\rho\pi}(0)=0.596$。